texts: How can a supermassive black hole cause so much energy to enlighten its matter when its massive gravity prevents light to escape?

texts:
To cite the German newpaper article Astronomen beobachten erwachendes Schwarzes Loch:

Das Materie-Monster sitzt den Angaben zufolge im Herzen der 42 Millionen Lichtjahre entfernten Polarring-Galaxie NGC 660, deren Aktivität innerhalb weniger Monate Hunderte Male zugenommen hatte.
Erst wenn die Massemonster große Mengen Materie verschlucken, werden sie aktiv. Bei diesem Prozess wird so viel Energie frei, dass die Materie hell aufleuchtet, bevor sie im Schwarzen Loch verschwindet und ein Teil von ihr in Form von Jets weit ins Weltall hinaus geschleudert wird.

This translates roughly to:

According to the data the matter-monster is in the middle of the 42 million light years far away polar ring galaxy NGC 660, whose activity has increased a lot in only a few months.
Only when these Matter-monsters swallow big amounts of matter, they become active. This process releases so much energy, that it brightly enlightens the matter, before it disappears inside the black hole. A part of the matter is flung out in the universe in the form of jets.

My physics teacher told me once, that a black hole is just a very small-sized and heavy object which has so much gravity that nothing at all, not even light can't escape of its gravity. This explanation is also supported by this SE.astronomy - If nothing travels at the speed of light, except light, how can a black hole also pull light into itself? question.

If a "normal" (not supermassive) black hole can already prevent light to escape, how can matter which is pulled into the black hole can produce energy/light which can't escape the gravity of the black hole?

How can a supermassive black hole be able to pull matter, but not the light photons of the energy?

Additionally: Why is part of the matter which is pulled into the black hole flung (i.e. accelerated) into the universe? I understand why this matter is maybe divided - the acceleration increases as far as i know quadratic, i.e. the differences in terms of the actual acceleration, in dependence of the location may be so huge that the matter can't be held together. But i don't understand why a part of the matter is accelerated in the exact opposite direction, as a force bigger as the gravity of the supermassive black hole would be needed. Therefore: Why is a part of the matter accelerated in the opposite direction (i.e. out of the black hole's gravity) than the other part?

Note: My physics education is rather limited. I know a bit about the Newtonian gravity and a bit about the theory of Conservation of energy. But that's all I know about physics.


texts: Telescope: Orion 09843 SpaceProbe 3,3 inch aperture(76mm), 700mm focal length, eyepieces - 25mm and 10mm focal lengths. Please tell me whether it is possible  to see nebula and  galaxies.


texts: Are there sufficient observational data to measure non-Newtonian perihelion advances of any Asteroid and Comet orbits?

texts:
Anomalous (i.e. not predicted from Newtonian theory) advances of the perihelion direction have been observed for many solar system planet orbits and have been accounted for by Einstein's General Relativity.

Basic Orbital elements have been obtained and published for many Asteroids and Comets.  But are the existing observational data on any Asteroids or Comets sufficient (in terms of accuracy and extent of observations) to determine/estimate rates of non-Newtonian perihelion advance and are any such determinations publically available?


texts: What inaccuracies are in this Stellarium depiction of the sky?

texts:
I found this depiction on Stellarium of the sky as seen from near the Apollo 12 landing site on January 11, 2131. The earth is the black circle in the arm of the Milky Way.

Here is a similar view with labels.

Assuming a person had a naked eye view of this, and the most of the light coming directly from the sun could be attenuated, what inaccuracies are evident in this image? As I understand it the colors to the Milky Way could not be seen by the naked eye. I take it the size of the objects are illustrative of apparent magnitude and not the visible size. Are there any others?
If the "night-sky" tag is not appropriate because this is not the view from Earth please remove or let me know and I'll remove it.
Here is the full screen shot, at horizontal FOV of 90°.

In regards to the sizes of the sun and the earth, at a narrower FOV Stellarium shows the earth as being substantially bigger than the sun.


texts: Mapping illumination to moon phase (font) icon

texts:
I use algorithms that give me the moon phase, age and illumination (and more) for a given timestamp and location. I am struggling to map that information to a (font) icon of the Moon Phases font. Each icon is an approximation because it ignores the rotation. Still, I'd like to map illumination (I guess?) to icon as precisely as possible.

As you can see above there are 13 characters/icons per half cycle; 26 characters a-z. However, new/full moon are represented by the numbers 0 and 1. Particularly there's a gap between m and n where the new moon is in reality. The font uses a-z and A-Z to distinguish between northern hemisphere and southern hemisphere (again, I guess).
Mental model
Illumination 100%                              0%                              100%

Moon         full                              new                             full

              |---------------------------------|--------------------------------|

Character     1            a - m                0             n - z              1

Assuming my mental model is correct this means (for the northern hemisphere)

13 characters plus 0/1 to distribute across the 0-100% illumination range
pick 0 if the illumination is <= 100/15 i.e. <= ~6.66%
pick 1 if the illumination is >= 100 - 100/15 i.e. >= 93.33%
if waning (waning gibbous, last quarter, waning crescent)

round(illumination/100 * 15) + 97 to find character index for a-m

if waxing

round(illumination/100 * 15) + 110 to find character index for n-z

Does that sound about correct?


texts: Where is the center point for the Supergalactic coordinate system?

texts:
I'm trying to build a 3D visualization of the Supergalactic coordinate system and couldn't find any reference to where the center point should be (the Sun, galactic center, the Earth, etc).

Also I already tried to look into some articles and books, but they only refer to the zero point related to the galactic coordinates.

Where should it be?

Could I use this model as the reference for the Supergalactic Coordinate system, starting to count the SGL (L) and SGB (B) from the yellow line?

It is still unclear to me if (l=137.37 b=0) indicates just the direction of the center of the Supergalactic Coordinates System.

Note: The Sun is being used as the center point.

Plano Galactico translates into Galactic Plane.

Centro Galactico translates into Galactic Center.


texts: How does an Echelle spectrograph put such a long, high resolution spectrum into a square-ish format?

texts:
In order to obtain a very high resolution spectrum to resolve closely spaced lines, or to measure doppler shits, spectrographs are operated with very high dispersion.

But photographic plates and CCDs usually have rectangular formats with aspect ratios not very far from square.

Echelle spectrographs can put a highly dispersed spectrum into this format, but how? This article explains to some extent, but a concise discussion here would also be helpful.


texts: What does less than one count from an x-ray detector mean? (Swift BAT detector)

texts:
I'm reading a paper about a recent x-ray burst from a suspected magnetar (A. Dai et al 2016) where they show a light curve of a burst that lasted about 10ms. (Their figure 1). The value of count rate for the peak of the burst from the graph is $6\text{ counts/s}$ over a timespan of less than $0.01s$. This corresponds to about $6*0.01=0.06 \text{ counts}$ for that time period. What does this mean? Is it not counts of photons? What is 0.06 photons? Is there a step in the data analysis I'm missing?

(Fig. 1 Swift/BAT mask-weighted light curves in different energy bands)


texts: Why did astronomers believe most or all stellar black holes had masses no greater than 15 solar masses?

texts:
The so-called 'mass gaps' for black holes, according to theoretical models, are between 2-5 solar masses and 50 to 150 solar masses.  (Actually, I have read that there is no good theoretical reason for the lower, 2 to 5 solar-mass gap....)
But, I have also read that astrophysicists were surprised to find black holes larger than 15 solar masses using the LIGO gravitational-wave Observatory....
For instance, from New Scientist:

Then there are stellar black holes. These are created in the gigantic explosions that end the life cycles of massive stars, and the closest to Earth is around 1,000 light years away. They tend to weigh in at between five to 15 solar masses, and they were the black holes that most astronomers had assumed LIGO would pick up. But the 2015 discovery only made sense if one of the colliding black holes was roughly 35 times the mass of the sun, while the other was around 30 times this mass.
Subsequent detections threw up more seemingly inexplicable black hole masses. The GW190814 signal involved one black hole that was too heavy, at around 23 solar masses, and one that was too light, at about 2.6 solar masses. Then there was GW190521, from a collision between black holes of 85 and 66 solar masses. “These observations are very hard to explain with astrophysical scenarios and they are quite easily explained with primordial black holes,” says Sébastien Clesse, a cosmologist at the University of Brussels in Belgium.

Read more: https://www.newscientist.com/article/mg24933280-100-is-there-an-ancient-black-hole-at-the-edge-of-the-solar-system/#ixzz6sOzdIpJW
But, WHY are they 'very hard to explain' in terms of conventional astrophysics?
I read elsewhere that, before LIGO, no stellar-black-holes had been detected above about 15.65 solar masses, but that reference did not say that none were expected above that mass....


texts: How to compare a Catadioptrics light asorbtion with a reflector?

texts:
I used to have a 6" Dobsonian reflector, and the next telescope I buy, I want it to have the equivlant of about a 11/12" dobsonian reflector.

I'm looking at this Nexstar VX 9.25 , it says 235mm aperature, but is thats more than what a 235mm reflector would acheive right? How close is to a 11/12" reflector?


texts:
We have Hubble's law:

$$v=Hd$$

where H is the Hubble parameter, which is decreasing in value, but it will be constant in the distant future. So, assuming the Standard Model of Cosmology holds true, will Hubble's law be accurate when the Hubble parameter becomes a constant?


texts: How is angular momentum transferred between a neutron star and its accretion disk?

texts:
Accreting neutron stars can either gain or loose angular momentum via interaction with their accretion disks. This leads to either spin-up or spin-down. Which of the two is the case, depends on the position at which the plasma couples to the magnetic field lines (see image). So far I kinda get it.
My question is: How exactly is the matter accelerated/decelerated when it "couples" to the magnetic field lines and how does this lead to transfer of angular momentum with the NS?
I guess, some magnetic fields lead to some Lorentz forces on some currents and eventually some torque will transfers angular momentum from the NS to the plasma (and the other way around); but how exactly?
I suspect some of the answers are included in the original work by Ghosh & Lamb 1979 (image below), but I have to admit some parts of their papers go a bit over my head.


texts: Does all of time exist and if so where is it?

texts:
I've recently learned about the theory of relativity and time.  I'm trying to understand it more.

My (basic) understanding is that there is no distinction between past present and future and that all of time already exists.

If this is true, what prevents us from seeing the past and the future? And/Or what causes us to only be able to see the "present"?


texts: Can gravitational waves pass through a black hole?

texts: As the title says, what happens when a gravitational wave approaches a black hole?  I would presume that something interesting happens because of the way spacetime works near black holes but I have no knowledge to back it up.


texts: Are we really seeing the asteroids from the past?

texts:
Is it actually relevant to study objects that are light years far? Because in theories we are actually seeing the past as the light takes years to reach us.

Lets say we are studying a asteroid that is going to hit as after several hundred years how can we confirm we are truly studying the actually position and everything of that object as we are seeing object from the past.


texts:
NASA developed SPIKE: Intelligent Scheduling of Hubble Space Telescope Observations (HST) and this.

My question is simple, is there a programming library, preferably in python or C#, to implement the algorithm? AFAIK  NASA never released their code.


texts: How does making a refracting telescope very long reduce the chromatic aberration of an uncorrected lens?

texts:
Below are two cropped views of "Johannes Hevelius's 8 inch telescope with an open work wood and wire "tube" that had a focal length of 150 feet to limit chromatic aberration." from Harvard University, Houghton Library, pga_typ_620_73_451_fig_aa (found here) the first of which I've zoomed and enhanced the contrast.
According to Wikipedia's Aerial telescope; Very long "tubed" telescopes:

Very long "tubed" telescopes
Telescopes built in the 17th and early 18th century used single element non-achromatic objective lenses that suffered from interfering rainbow halos (chromatic aberration) introduced by the non-uniform refractive properties of single glass lenses. This degraded the quality of the images they produced. Telescope makers from that era found that very long focal length objectives had no appreciable chromatic aberration (the uncorrected chromatic aberration fell within the large diffraction pattern at focus). They also realized that when they doubled the diameter of their objectives they had to make the objective's focal length 4 times as long (focal length had to be squared) to achieve the same amount of minimal chromatic aberration. As the objective diameter of these refracting telescopes was increased to gather more light and resolve finer detail they began to have focal lengths as long as 150 feet. Besides having very long tubes, these telescopes needed scaffolding or long masts and cranes to hold them up. Their value as research tools was minimal since the telescope's support frame and tube flexed and vibrated in the slightest breeze and sometimes collapsed altogether.

A refractor's primary lens produces an image because the angle it deflects is proportional to the distance $x$ from the center of the lens of focal length $f$ as
$$\theta \approx x/f$$.
For a dispersive material the deflection at a given point on the lens varies with wavelength, and therefore the focal length of the lens varies with wavelength.
 Source
This is called chromatic aberration and its severity for a given type of glass is often expressed by its abbe number.
Question: Is there a simple mathematical way to explain how making the focal length longer could possibly improve a telescope's performance by decreasing the impact of chromatic aberration on its performance?
Or do I misunderstand what the benefits are to making these very long telescopes?


texts: Calculating distance of comet C/2019 Y4 (ATLAS)

texts:
SO, I decided I would take some pictures of the comet C/2019 Y4 last night. Afterwards, I thought I would try and do a rough estimation of distance based on my observations. I don't have any fancy measuring tools, so a few approximations were made, but my result was way off. I've clearly done something wrong and was hoping someone could point out where I have gone wrong and correct me.

So, I basically layered my first picture over the second in photoshop and marked the start and end position over the course of 1 hour.

I apologise for the poor photo, the exposures were short and I haven't done any processing as I was only interested in the position.

So,to me, it looks like it has moved approximately he same distance as the 2 stars to the right. These are TYC 4360-0254-1 and TYC 4360-1679-1 according to Sky Safari Pro.

I used the measurement tool in the app to measure the distance in arc-minutes, which gave me 1'55.1"

I converted this into degrees using Google, which gave me 0.0258333333 degrees.

I then decided to work out the approximate distance between my start and end points by using my latitude to work out the speed the earth was rotating (cos(latitude) x 1670) which I found HERE.

My latitude is approx 50.82N, so I got my speed at 1055.04km. I used that as a distance. I now have a triangle with a base of 1055.04km and a top angle of 0.02583 degrees.

I turned this into a right-angle triangle by putting a line down the middle. I can now work out all 3 angles. I have 90, 0.010129 (half the original angle) and 89.987 (90-0.010129) I also have an opposite, adjacent and hypotenuse. I only know the adjacent which is half my original distance (527.52km), and I want to find the Opposite.

Using SOHCAHTOA, I can say tan(89) = opp/adj, thus opp = 527.52 x tan(89.987) which gives me 2,324,974.545km.

Sky safari gives a distance of 153.1 million km.

So where did I go wrong? Was it because of poor approximations? I know that the linear distance for the adjacent side isn't quite accurate because of earth curve, and I know the comet was also moving, and I know my measurement of the start and end position wasn't too accurate, but I was hoping to at least get within 10%, so I think I must have gone wrong somewhere in my method, rather than poor approximations.

I do hope I have put enough effort in for this to be considered a good question. I have tried re-measuring and double checking, but if there is any other info people need, then by all means, ask and I'll do what I can

EDIT

Because of the comment by barrycarter, I realised I had forgotten the movement of earth itself. As this is approximately 107207km/h, I included this in my calculations and ended up overshooting and getting 238,577,507km.

So, I made tiny adjustments to my parallax angle, and if I change this slightly, then I get very different answers.

Based on that, is it possible my crude measurement of the parallax angle is to blame?


texts: Do more massive stars become larger or smaller white dwarfs?

texts: I wonder whether e.g. stars more massive than the Sun (but below the mass where they'd go supernova) would become larger or smaller white dwarfs than a white dwarf Sun. Since Procyon B is larger than the more massive Sirius B, I suppose the more massive the star the smaller its remnant white dwarf would become. Am I right and if so, why is it like this?


texts:
I pointed my telescope
(50mm aperture, 500mm focal length, 4mm eyepiece, image taken through a window)
at Venus and saw this:

What is it? I don't think this is Uranus or Neptune as my telescope is very bad. I haven't increased the image size too much and it was 6 A.M. (UTC+3, EEST)


texts: Would you recommend this telescope to a beginner?

texts:
Celestron Astro FI-5 125 mm f/10 Schmidt-Cassegrain with a computerized altitude-azimuth single fork mount

https://www.celestron.com/products/astro-fi-5-schmidt-cassegrain-telescope
https://www.amazon.it/dp/B06WD5JVJ8/ref=cm_sw_r_other_apa_i_kxXnEb3XD5AR4

A friend of mine wants to buy a telescope and begins observing in person. The area won't be among the most polluted in Italy, say the Milky Way is often visible by eyes and she already gets some traces of it while playing with modern smartphone and the apps they are equipped with.

She has spotted the above telescope.

Now, both me and my friend like amateur astronomy but we totally lack of knowledge on observational backyard astronomy and the related optics.

Would the linked telescope be a good starting point for a total beginner? Does it allow for the observation of nebulae and Andromeda while being OK for planetary seeing as well?

Alternatively feel free to signal if this can be a sort of overshooting. Though the budget is not an issue, considering that it just to begin is somehow mandatory.

What I began to consider is avoiding to invest some money in something that requires a very very dark environment in order to be used to see diffused objects. The telescope will stay, at least most of the times, in a dark extraurban area nevertheless close to several towns.

Would you suggest this scope or is there something making it not a good or reasonable choice for beginners?

PS beginning astrophotography is also considered, it can be as simple as having a smartphone mount. But playing with smartphones is how we became enthusiastic about astronomy and photography.


texts: Why don't we see evidence of glaciation on Mars, similar to Earth's Ice Ages?

texts:
With all recent NASA activity surrounding Mars manned missions, it is surprising that given Mars orbital distance from Sun that there is not evidence of massive glaciation similar to Earth's Ice Ages. Also Mars allegedly has erratic Obliquity anything from 11 - 28 degree swings which would obviously affect seasonal changes. Is this a fact (where's the evidence) or "scientific fable".

Interesting replies - due to implications of erratic obliquity, hopefully NASA have a probe recording changes.


texts: How much of a difference do good lenses make?

texts:
I recently purchased a Celestron PowerSeeker 114EQ and with it I got three lenses (which I assume are low quality), a 4mm, a 20mm and a 3 x Barlow.

I can get pretty decent views of the moon but a very blurry, small view of Jupiter with the 4mm and Barlow.  I can see the color of the storm rings for example, but barely.  I've not had a chance to have a go at Saturn yet.  A view similar to this...

I've been reading up on this and was looking at purchasing a 4-8mm Plössl lens but I'm not sure if the lens is my weak spot or some other aspect of the telescope.
Another thing to note is that I've been using it in a pretty bright street, looking up very close to street lights.  I've not had a chance to take out somewhere with less light pollution.

So what I'm asking is, how much difference would a lens upgrade make, specifically to my image quality?


texts: What's that limit, where we start to see infrared galaxies?

texts:
All the nearby galaxies we see come in visible range, many are visible from ground based telescopes. And the farthest galaxy that hubble discovered recently, 13.4 billion light years away is in infra red.
Was this Galaxy ever in visible part of spectrum?
How long will it take galaxies like andromeda or whirlpool to go infrared so that they won't be visible to us if we are not using in infraRed lens?
What's the specific limit where the light makes transition from visible to infrared part of spectrum?


texts: Is the moon inside earth’s atmosphere? If so, what are the consequences?

texts:
Recently, a paper was published claiming that the Earth’s atmosphere extends far beyond the Moon. This has been reported on by a number of news sources and websites, including the ESA, Business Insider, Space.com, and EarthSky.org.

If these findings are true, how does this affect the current understanding related to the measured atmospheric pressure, the currently accepted pressure in space between the Earth and the Moon, the pressure on the Moon, the effect of Earth's gravity on the atmosphere, and Earth's ability to maintain this extensive atmosphere while traveling through the Solar System? Is the atmosphere gradually lost or replenished?

Image credit: European Space Agency


texts: How do you refer to comparative temperature?

texts:
Earth's average surface temperature is about 288 K.  If we had a hypothetical exoplanet with a surface temperature of 300 K, this would be about 4% higher than Earth's.
Because we say Earth radii and Earth masses, would we refer to this as 1.04 Earth temperatures?  Or, how about 1.04 Earth's temperature?  $1.04 \cdot T_⊕$?  Is there a standard in astronomy to use?


texts: What factors influence a star's temperature and density?

texts:
Assuming a relatively even proportion of mass and radius, a 0.25 solar mass and radius star would have a density of 22.5003 g/cm³, or about 16 times our Sun's density.
However, there is obviously a range of densities that this sized red dwarf could have.  One of the primary factors is its temperature, with cooler meaning a higher density.
My question is three-pronged: what would increase or decrease this sized star's temperature, how would this impact its density, and what factors other than temperature would increase or decrease this star's density?


texts:
This answer to How precise are the observational measurements for the speed of gravity? says:

...in 2013 a Chinese group built a model using Earth's tides that helped them narrow it down.

... [T]he speeds of gravity are from 0.93 to 1.05 times the speed of light with a relative error of about 5%. This provides first set of strong evidences to show that the speed of gravity is the same as the speed of light.

This is so far the most accurate measurement I've seen.  See the paper for more.
In the near future, LIGO may be able to provide more accurate measurements by comparing the distance among detectors and the delay of observation.

In case the links break, the papers are:

"Observational evidences for the speed of the gravity based on the Earth tide" TANG KeYun et al. Chinese Science Bulletin, February 2013 Vol.58 No.4-5: 474-477 doi: 10.1007/s11434-012-5603-3
"Bounding the speed of gravity with gravitational wave observations" Neil Cornish, Diego Blas, Germano Nardini 2017,  https://arxiv.org/abs/1707.06101

update: As noted in @amateurAstro's comment and linked well-sourced answer the time between a gravitational wave detection and X-ray burst of GW170817 and GRB 170817A constrains the difference between the speed of gravity and the speed of light to be "...between $-3 \times  10^{-15}$ and $+7 \times 10^{-16}$ times the speed of light..."
So my updated question is:
Question: Have more recent LIGO/VIRGO gravitational wave measurements narrowed down the speed of gravity further?


texts: Are there examples of the effect of shock waves on chemical evolution in of interstellar medium or circumstellar medium?

texts: Are there any examples of calculations or observations of suspected effects of shock waves on chemical evolution in interstellar medium or circumstellar medium?


texts:
Can SETI certify whether or not  Proxima b is inhabited by beings using electromagnetic communication?

By certify I mean by past, present or future observations using technologies available.


texts: Why does moon's highest altitude change during the year

texts:
I came across a question in which moon's highest altitude had to be calculated as seen from a certain latitude, also the month and the hour and the constellation in which moon would be in had to be calculated......

I could not understand why or how would moons path change during the year


texts: How far into the future can we go by traveling close to a black hole?

texts:
If we sent someone on a path that passed as near as possible to a black hole without getting pulled in, how far into the future would they go due to time dilation?  Let's assume the black hole is 5 solar masses (I am assuming the mass will affect the calculation).  I would like to know from two considerations:

An observer that can survive anything (e.g. ideal case)
The forces that a human can tolerate (e.g. a human would not be able to get as close to a black hole as would be ideal)


texts: if the big bang only expanded the universe when and how did it originate?

texts: If the big bang expanded the universe from a singularity point, that means that there was matter before, so where and how did matter form for the first time if it's even possible to know such a thing?


texts:
In general, are carbonaceous chondrites (CC) or comets more water rich?

I know that evidence has suggested that both CC and comets are partly composed of water, but which body is generally more water rich?


texts: How old would I be if I travelled 1000 light years in one year

texts: If I were to travel 1000 light-years, and witness only 1 year elapse in my frame of reference, how much time would have passed in the frame of reference of the Earth?


texts: What are some examples of routine human activity times for certain cultures/peopes that are based on the position of the sun?

texts: What are some examples of timekeeping that are based on the height/angle/position of the sun. Two examples that come to mind are the times of the Islamic prayers times and the golden hour in photography.


texts: Information on Planetary nebula formed from the death of our star the 'Sun'!

texts:
I want to know the expansion rate, composition, mass and density of hydrogen present of a Planetary nebula similar to that which will be formed after the death of our star the sun.

Knowing these data is important for me to do some calculations.


texts: Are there any stars visible to the naked eye whose position, over a normal human lifetime, can be seen to have changed (relative to other stars in the vicinity)?


texts: Why are helium resonance lines called "resonance lines"?

texts:
Examples of the use of the term:

Formation of the helium extreme-UV resonance lines
On the Formation of the Resonance Lines of Helium in the Sun (unpaywalled)
Formation of the helium EUV resonance lines.

When I hear of a resonant state I think of a free particle incident on a potential where it spends a lot of time then leaves, but the electrons responsible for these lines (HeI 584 Å, HeII 304 Å) start in bound states below their binding energy and are just transitions from one bound state to another.

Since most emission lines from atomic transitions are not called resonance lines:

Why are these lines different?
What is particularly resonant about them?


texts:
I'm just starting a project to analyze some of the images obtained from the Dark Energy Survey (DES), and I'd like to get some of the COADD images from the SV data.

For example, this paper: https://arxiv.org/pdf/1512.03062v1.pdf shows a series of images that are apparently from the 'DESDM database of coadd objects'.  Just looking at image (a) on page 3 of the paper, I can find images in the DES Y1 data from NOAO Science Archive at http://archive.noao.edu/ that show the objects in image (a) from the paper, but they are individual exposures - I can't find any COADDed images.

Can anyone tell me how to get these COADD images?


texts:
This excellent answer points to ESPRESSO, - Echelle SPectrograph for Rocky Exoplanets and Stable Spectroscopic Observations. From there I looked at the Instrument Description and Performance page.

The page describes three parts or th esystem:

Coudé Trains (transporting light from each of the VLT's four telescopes)
Front Ends (corrections, stabilizations, fiber pick-up)
Spectrograph (fiber output, pupil slicer, Echelle grating, collimator, dichroic splitter, Red and Blue cameras)

I'm wondering what the pupil slicer is, and how it works exactly.

  At the entrance of the spectrograph, an anamorphic pupil slicing unit (APSU) shapes the beam in order to compress the beam in cross-dispersion direction but not in main-dispersion direction, where high resolving power needs to be achieved. In the latter direction, however, the pupil is sliced and superimposed on the echelle grating to minimize its size. The rectangular white-pupil is then re-imaged and compressed by the anamorphic VPH grism.

I'm familliar with the basics of how an Echelle spectrograph works, and as far as anamorphic optics, I understand this to mean that not all of the elements are not cylindrically symmetric so that the size and divergence changes in one plane is different than in the perpendicular plane. (Classic example is Anamorphic format).

Question: What is a pupil slicer, and how does it work with anamorphic optics in VLT's ESPRESSO Echelle spectrograph?

below: The Spectrograph itself. Light enters from the right from an optical fiber, and the anamorphic pupil slicer (whatever that is) forms a diverging beam to illuminate the entire Echelle grating (beam shown in gray) via the collimator. Everything else in this drawing is post-grating.


texts: How to use a telescope to find a specific celestial body?

texts:
I am a beginner interested in astronomy. I bought a Celestron AstroMaster 130EQ telescope. It's a Newtonian Reflector and it's not computerised. I did manage to see the Moon in some magnifications but my real question is this:

Suppose I want to see Proxima Centauri and I know it's coordinates, like Right ascension is 14h 29m 43.0s and Declination is -62° 40' 46". Having three analogue dials on my telescope (picture from the front) (zoomed in), how do I adjust my telescope with the help of the dials with the coordinates so I can view them from my telescope?

If I am wrong that these are the dials I have to use to adjust my telescope to the coordinates then please explain how.

I hope this question will also be useful to other amateur astronomers. Thanks.


texts: Issues in dimensions and slicing while plotting contours over a FITS Image in Astronomical Plotting Library in python (APLpy)

texts:
I have been trying to plot the contours of a FITS image over itself in APLpy. The image was created in AIPS, and has dimensions (1024,1024,1,1), viz., right ascension (RA--SIN), declination (DEC--SIN), frequency (FREQ), and Stokes (STOKES). I tried to load the FITS image and plot the contours of this image over itself, using the following commands -
baseimg = aplpy.FITSFigure('FILENAME.FITS')
baseimg.show_contour('FILENAME.FITS')

This returned the error WCS has more than 2 pixel dimensions, so 'slices' should be set.
So, I specified the dimensions and slices while loading the FITS image, as-
baseimg = aplpy.FITSFigure('FILENAME.FITS', dimensions=[0,1],slices=[0,0])

i.e., specifying RA and DEC as the x and y axes respectively, and using the only available value of Frequency and Stokes as the slice. Trying to plot contour again as-
baseimg.show_contour('FILENAME.FITS')

or
baseimg.show_contour('FILENAME.FITS', dimensions=[0,1],slices=[0,0])

again gives the same error WCS has more than 2 pixel dimensions, so 'slices' should be set.
I am stumped as to what I am doing wrong here. I am absolutely new to APLpy. Any help is immensely appreciated.


texts: Given a star's mass, age, and composition, how do I calculate the rest of its properties?

texts:
If I'm given a star's starting mass, starting composition (metallicity), and its current age, How do I calculate the star's luminosity, current mass, and radius?
I want to know how to do this for any star, from the minimum size of 0.08 solar masses all the way up to stars 100-150 solar masses for a personal project.

I know that there are equations that relate these things, but my desperate googling has only found bits and pieces of the answer I'm seeking. Also, many of the equations I've found only apply to stars within a certain mass range (usually near the sun.)
I would seriously appreciate some guidance from an expert in the field.


texts: What came first: the Sun shining or the existence of helium?

texts:
This seems to be a chicken and egg problem, the sun begins shining due to hydrogen becoming helium, but it's odd that there was no helium initially without the stars.

Is my logic flawed?

(Note: First year astronomy student)


texts: If I want to learn about astrophysics, should I study up on mathematics?

texts:
I am currently reading A Brief History of Time and while the book itself does not contain much mathematics in it, I want to learn more about the concepts Prof. Hawkings talks about more in-depth.

Now I am aware that I will never get the expansive knowledge that a university tuition in the field would give me, but I have already branched off into something else that does not allow me to pursue that field even if I really wanted to so I want to make do. (I also understand that any knowledge I do get will be basically useless to me, but I love space that much that, in spirit, the knowledge would feel useful to me.)

My question is, before I read books more technical, should I brush up on my math? I am aware that a more applicable subject like physics has more correlation with what I am interested in, but I don't want to read about physics if I have little to no knowledge what the hell each equation means. (Also, how I will learn is through online courses/websites/books. I know it is not the ideal way to go about it, but again, I will do what I can.)

Of course, if you believe I should somehow go back a few years and try my hardest at physics and follow the most tried path, I am all ears. It is just that I am now going to a technical college for IT and if I want to leave, I would have to spend a lot more time in education than most - meaning (as I live in the UK) will probably have to pay extra when I pass a certain age.

I know this question is not exactly linked to astrophysics, but I do not know where else to ask it. If I had read A Brief History of Time earlier in my life, I would not be in this sticky situation. Thanks in advance.

(ADDITION: I have always had a love for space and I was interested in physics, but my teacher was uninspiring and I was going through a tough period in my life. I am willing to work towards it now, even if my teacher is the worse thing to ever exist.)


texts: Could S5-HVS1 conceivably still hold on to any planets?

texts: If the star (S5-HVS1) has been accelerated to 1,700 km/s by a close encounter with the super massive black hole at the centre of our galaxy (Sagittarius A*) what would happen to any planets orbiting this star? Would they have been stripped off by the massive acceleration or could any conceivably still be in orbit? Presumably any orbiting bodies would be significantly perturbed!? see https://www.sciencealert.com/our-bossy-black-hole-kicked-out-a-star-and-it-s-shooting-through-the-galaxy-insanely-fast


texts: Lightkurve nan values after bin light curve

texts:
I am using lightkurve 2.0.2 library with Python 3.8.5 and astropy 4.2 for processing exoplanet transits. However when I want to bin light curve to fixed number of points, all values in light_curve.flux except first two are nan. What I am doing wrong?
The purpose of code bellow is to obtain transit of Kepler-10 a from light curve of Kepler-10.
import lightkurve as lk  # Import lighkurve package

tp = lk.search_targetpixelfile("Kepler-10", mission="Kepler", exptime="long", quarter=1).download()  # Download target pixel for Kepler-10
lc = tp.to_lightcurve().flatten().remove_outliers()  # Convert target pixel to light curve
fold = lc.fold(0.837)  # Fold light curve to period of Kepler-10 a (0.837 days)
bin = fold.bin(n_bins=101)  # Bin light curve, so it should contains only 101 points.

print(bin.flux)  # [0.99999749 0.99999977 nan nan nan nan nan nan nan ... nan nan nan nan]

lc and fold are valid light curves without NaN values. E. g. fold looks like this:

So if there is any problem, it should be on line with fold.bin. Also, this is not problem only for Kepler-10.


texts:
I am new to stellar astrophysics and trying to understand the energy transports in the interior of stars.
Can the energy transport by radiation occur in the convection region of a star?
Here are my thoughts:
Since the gas pressure in the convection region dominates, $\nabla_{\rm gas}$ $<$ $\nabla_{\rm radiative}$, so energy transport by radiation will not occur in the region.
Please correct me if I am wrong.


texts: Expanding our observable universe suggestion

texts:
Firstly, regarding the observable universe there is a certain radius of a circle, and we cannot see further than that. It is understandable, that due to photons travelling at a certain speed we can only see that far. But question is: "What happens with photons that might arrive later to our vision?", meaning outside our "ring" of the observable universe, to my understanding we could detect also photons or radiation coming from there, meaning that our radius of the visible universe is expanding, in the sense of areas now, where we can have layers of certain visibility and with a percentage of "accuracy" and not a static radius, i.e. "x light years beyond the radius the existence of one y object has been confirmed due to late photons coming to our vision. There might or might not be more around it but we have no certainty". Understanding human life is too short to experience that change, these humans might be living some thousands of years from now. Until here I have considered a static model, I haven't taken into account universe expansion yet.
When the universe expansion speed is put into the equation, things change. If the universe expansion is faster than the speed of light, we would be "losing ground" in visibility, meaning more objects would be leaving our radius than the ones coming, however nothing is faster than the speed of light, meaning that the universe expansion is smaller than speed of light (unconfirmed quotation), thus in reality to me, our vision should be expanding, but slower than the static model I described a little earlier.
On the other hand, at the edge of our imaginary ring, we can also have objects popping in and out from time to time. In this manner we can also create an uncertain map of what was and what will be in the outer ring of our observable universe, thus expanding our vision, and over time this map will be more certain.
Now, I haven't done the math, nor am I certain of many of my quotations, so please don't be angry at me, I am just a curious human being trying to learn more about our universe :)


texts: How can I estimate the initial luminosity of a SNIa given initial mass of Ni-56?

texts:
The initial portion (and peak) of a SNIa's light curve is powered by the $\beta$-decay reaction:
$$ ^{56}Ni \rightarrow ^{56}Co + e^+ + \nu_e + \gamma $$
Supposing we know how much Ni-56 is created in the supernova (i.e., an initial mass of Ni-56), how can I go about estimating the luminosity peak? The half-life of Ni-56 is 6.1 days, if that's relevant.
Does it make sense if I just look up/calculate the energy released in this reaction, multiply it by the number of Ni-56 atoms required to comprise the given initial mass, and call that the luminosity? Any other better ideas?


texts: Is it possible to steer the sight of a Liquid Mirror Telescope using a plain mirror scheme? If yes, why hasn't it been done?

texts:
I have read about Liquid Mirror Telescopes in a number of places, and according to these sources, a major disadvantage of these telescopes is that they can only "see" straight up.

In a nutshell, the usually very expensive primary mirror is replaced with a rotating mercury container. The mercury surface will become parabolic with the rotation and earth's gravity, and a camera is placed in the focal point of the parabola (straight above the container). Since the parabolic shape depends on gravity, the primary cannot be tilted and the telescope can only point straight up.

My question is: couldn't one use a mirror scheme to steer the sight of this telescope? For example a pair of big plain mirrors a bit above the focal point, working similarly to a periscope. Then one could change the angles of these two plain mirrors and point to different directions in the sky.

I am assuming a large plain mirror is much cheaper than a parabolic mirror of the same size.

Has this been done? If not, why?


texts: Can close binaries have a very eccentric orbit?

texts:
For example, are there binaries with an orbital period < 5 day  and that are very eccentric?

What kind of factors could slow down orbital circularisation?

Are there examples of binaries with p<5day and e>0.1?


texts: If the Universe is flat and expanding at the speed of light, that must mean that we could never leave it, because one would have to travel faster than the speed of light which is not possible. However, what about going straight up or down ? The distance is less and if the Universe is not expanding in depth but only sideways then it would be possible to exit. Could we then find another Universe once we have gone out of this one ?


texts: When the set of official dwarf planets is expected to increase?

texts: When the set of official dwarf planets is expected to increase or new bodies considered for inclusion?


texts:
Why can primordial tensor perturbations of the CMB be ascribed to gravitational waves? Is this attribution unique, or are there other mechanisms that could lead to the excitation of tensor modes?

In an explanation I have read recently that gravitational waves turn the E-modes into the now observed B-modes somehow, but I don't understand this. So can somebody give a more detailed explanation of this interaction of gravitational waves with the CMB?

LaTeX and equations are welcome and appreciated :-)


texts: Is it possible to calculate the time of day given latitude, longitude and solar elevation angles (zenith, azimuth, elevation)?

texts:
I am trying to determine the time of day of some images I have.  I know the lat/lon, the day and year of image.  I also know the 3 solar angles (zenith, azimuth, and elevation).  Is there MATLAB or any other code that can do this calculation?

Thanks!


texts: This may be a very stupid question, as I know little about astrophysics, but if solids like Aerogel can float in gasses like sodium hexafluoride, could there be pressures high enough on gas giants to compress a gas to the point where solid particles such as dust collide and create floating landmasses?


texts: Does The ISW Effect Predict Net Redshift Over Distance?

texts:
The Integrated Sachs–Wolfe (ISW) effect is concerned primarily with the study of the Cosmic Background Microwave Radiation (CMBR), but seems to demonstrate that photons passing through voids suffer a net energy loss resulting in redshift, or can be blueshifted passing through high-density regions.

If a photon traveled long enough through alternating high and low density regions of space, can we assume that (depending upon the total ratio of density to void in all the regions traversed) our photon might well accumulate a substantial net gravitational redshift or blueshift after traveling a vast distance?


texts: Does the luminosity of a star on its main sequence increase or remain approximately constant?

texts:
From my understanding, the luminosity of a main sequence star should increase because, in its core, hydrogen is being burnt into helium which means that the number density of hydrogen decreases and the temperature increases and from the Stefan–Boltzmann law, the temperature is proportional to the luminosity so the luminosity of a star should increase while it's on the main sequence phase of evolution.

Please correct me if my reasoning is incorrect.


texts: In the lambda-CDM model describing an accelerating Universe, the Hubble parameter is currently decreasing with time. Will it continue to decrease forever?


texts: How to calculate the true length of day on a celestial body?

texts:
When I only know the sidereal rotation period, how do I determine the true length of day on a body?

We know the Earth's sidereal day doesn't have full 24 hrs unlike the true length of day. It's similar on Mars where the sidereal day isn't as long as a Sol (about 24 hrs 40 min) either. So how do we calculate the true length of day on a planet?

Let's do it on the example of the planetoid Ceres: its sidereal rotation period is 9 hrs 4 min and 27 sec. How do we calculate the true length of day on Ceres?


texts: Does the cosmic microwave background change over time?

texts:
Does the cosmic microwave background pattern change over time?  I would assume it is getting "cooler" as in more redshifted as time passes, but I am more interested if the pattern on the background, as depicted below changes.  I would expect we would see something like the cosmic microwave background retreating one light year (or possibly further due to inflation) every year, and it would be neat if we could make a "3D map" of the background as time passes (e.g. take an image of it every year).

http://lambda.gsfc.nasa.gov/product/map/dr5/map_images/wmap_planck/wmap_planck_ilc_300uK_med.png


texts: Does gravity repel when dark energy is involved?

texts:
So I am currently reading the book We have no idea by Jorge Cham and Daniel Whiteson.
In one of their chapters they talk about how gravity is a force that only attracts and doesn't repel, most of the time. Dark energy is what makes up 68% of the universe and the only way we know it exists is from its rapid expansion.

The expansion isn't slowing down, however, it is speeding up. Gravity is a force that is said to be a force that only attracts and doesn't repel, unlike electromagnetism, the weak force and the strong force. Gravity should be slowing down that expansion, and I am wondering if anyone can explain this or is this concept out of our reach.


texts: How to do logarithmic wavelength binning (in Python) in order to find redshift?

texts:
In Tonry and Davis (1979), p.1513, they formulated a cross-correlation method for extracting velocity redshifts:

Theory of Correlation Analysis
a) Introduction
Let $g(n)$ be the spectrum of a galaxy whose redshift and velocity dispersion are to be found and let $t(n)$ be a template spectrum of zero redshift and instrumentally broadened stellar-line profiles. These spectra are discretely sampled into $N$ bins, labeeled by bin number $n$; the relationship between wavelength and bin number is
$$n = A \ln \lambda + B$$
Because the spectra are binned linearly with $\ln \lambda$ a velocity redshift is a uniform linear shift. The spectra are assumed periodic with period $N$ [...]

They bin the linear spectra into logarithmic wavelength scale. Similar work was done by Baldry et. al (2014) and I have inserted relevant excerpt from TD79. I understand that log wavelength binning is a pre-requisite of cross-correlation procedure.
I have been trying to follow this approach and trying to rebin the linear spectra (3000 to 9000 Angstroms) in equal intervals of log wavelength. Could someone please give me a guidance about how to do this logarithmic re-binning  in Python?
Here the text as picture:


texts: Considering that the moon’s gravitational pull on earth is so weak- we need special instruments to detect it- how does it cause the tides?

texts: That the moon’s gravitational pull is responsible for the tides is established. However, if we want to detect the moon’s gravitational pull on earth, this is very challenging. This seems to be a paradox considering the enormous force needed to drive the tide.


texts: What fraction of matter is not bound to the galaxies, groups and clusters that we see?

texts:
We know that most of the matter in the universe has collapsed into galaxies and galaxies into groups and clusters and that a lot of matter is presently in clusters between the galaxies.  But, what fraction of total matter is not represented by these discrete observed entities?  Some dark matter may have velocities too high to fall into halos perhaps from tidal tails that escape mergers.  There must be some relic medium in voids with a density too low to form galaxies.  Some halos may be too small to form stars.  Does all of this add up to a significant intergalactic medium (IGM)?  Do n-body simulations give a number for this?
One might think that we could get the answer to this question by adding up all the known mass in the nearby universe and subtracting it from the CMB derived mean density of the universe times the volume used.  But some recent observational studies are suggesting that the local density is well below the mean density and that this is the cause of the Hubble Constant discrepancy.


texts: What colours can rocky planets (or moons) have

texts:
I am currently working on a simple program to randomly generate and display rocky exoplanets (for a space based strategy game), but I am having some problems figuring out what colour the rocks of rocky planets may or may not have.
Specifically, I am thinking of what natural colours may be so dominantly found on the surface of a planet or moon, that the whole planet or moon, seen from space would seem to be (completely or partially) that colour, which is not made out of ice, and which neither has oceans nor life.
As far as I can tell from looking at pictures of the not lifebearing rocky planets, dwarf planets and moons in our solar system, it seems that red and yellow colors are dominant on larger bodies such as Mars, Venus or Io (maybe because their atmosphere cause oxidation of metals on the surface, or in Io's case volcanic activities as pointed out by Phiteros):

All while smaller bodies such as the Moon or Ceres are completely grey:

Therefore my current approach is to make sure the red component of the RGB colour of the planets is the biggest, the green the second biggest and the blue the smallest.
However just the fact that there aren't any rocky planets or moons in our solar system made of blue and green rock, doesn't mean that they can't possibly exist.
Therefore my question is: is my assumption that rocky planets tend to be mostly red or yellow correct, or are there any good logical arguments for that predominantly blue, green or purple rocky planets could exist.
Edit
Maybe i was a little to vargue on defining colour; i was thinking about the »diffuse colour« (sometimes called »albedo colour«) input, used in the openGL shader that i am using to display the planets; this colour is however the same as something not very reflective (like planets) has when under white light.


texts: How to compute for Distance Modulus' uncertainty/ies?

texts:
This is rather a short question. As we know of;
Distance Modulus (DM) $\mu = 5 \log d - 5$
If $d = 168_{-14.9}^{+27.5}$ pc ($3\sigma$ value), how can I possibly compute for $\mu$'s uncertainty?
P.S. Perhaps I need to multiply those $\pm$ values to a 'some constant'(?)
Thanks a lot and clear skies.


texts: What elements and compounds would be present in a red gas giant?

texts: What would give a gas giant a red color (dark or light)?


texts: Was the solar system flat before the planets formed? Or does the Kozai-Lidov mechanism flatten orbits after the gas giants form?

texts: An astronomer living on Jupiter measures the orbits of the inner planets against Jupiter's ecliptic. Their inclinations are; Mercury 5.7 deg. Venus 2.1 deg. Earth 1.3 deg. Mars 0.6 deg.   It looks like Jupiter attracts smaller planets towards its own ecliptic.   If the original nebula was Oort cloud shaped, then the Sun and planets were assembled from components that had random orbital inclinations.  The "missing" momentum in the angular momentum problem was used up in the assembly of the solar system


texts: What is the formulat to compute King tracking rate for a given set of topocentric coordinates?

texts:
Canbury Tech has a good background on King tracking rate, which approximates the average sidereal motion of a refracted star across the sky. Most amateur telescope mounts have some sort of notion of this "average" rate, which is generally about 15.037 arc seconds per second.

However, King actually produced a formula that would allow the rate to be precisely calculated for a given set of sky coordinates. Modern microprocessor controlled mounts ought to be able to make use of this technique, but many don't. As the author of telescope drive software, I'd like to incorporate this feature into my work, but I don't seem to be able to locate the forumula. BBAstroDesigns has a calculator for this on their web site, but the don't show the formula anywhere.

Can anyone enlighten me as to how to compute this value?


texts: Where to get Polaris Right ascension value from

texts:
To calculate for example the polaris hour angle I use this formula to calculate polaris hour angle.

τ = θ - α

τ= hour angle

θ= sideral time

α= polaris RA (~ 2h32m)

But where does the α=2h32m come from? Is there a list? Does this change somehow over time?
Is my understanding correct that this is the time where polaris crosses the upper meridian at Greenwich?


texts: What conditions would lead to this event around the black hole in the Pictor A galaxy?

texts:
This is a picture of a jet of particles exiting the supermassive black hole in the center of Pictor A galaxy at nearly the speed of light. Source

This event is supposedly created from a black hole of 40 million solar masses. The full quote here:

  The newly released picture shows the terrifying power of an actual
  supermassive black hole located in the galaxy Pictor A, some 500
  million light years distant.  This black hole is about 40 million
  times the mass of the Sun (that’s about 10 times larger than the black
  hole at the center of our own galaxy), and if it were to replace the
  Sun within our Solar System, its event horizon would swallow the
  orbits of both Mercury and Venus.

Now a quick search to Wikipedia would show a abundance of supermassive black holes many, many times larger than that supermassive black hole as well as a few that are around the same mass as that.

To my question: What set of special conditions that surround this particular supermassive black hole such that it is capable of creating this spectacular event?

Edit for clarity: By this I meant the jet and the hotspot.


texts: Is there a strict chronological order that determines the shape of galaxies?

texts: Assuming no collision happens, do all elliptical galaxies eventually become spiral? Also, when a galaxy becomes spiral or barred spiral, can it switch between these shapes or is it set forever?


texts: Does Polaris have a trail in the sky timelapse?

texts:
I came across few sources that claim Polaris movement cannot be observed with the naked eye. But then, I saw images of the star trails (timelapse), and they clearly show Polaris not quite at the true north and moving around the Earth's axis with a radius that is very visible. See for instance the following images:

However, this image from Wikipedia does not show a trail for Polaris:

What am I missing here?


texts: About how many revolutions has the Earth made around the sun?

texts:
The Earth is about 4.543 billion years old.
However, the length of a year can be changed by anything from an impact to a natural cycle of orbit changes to a slow drift toward or away from the sun to the tug of a nearby body.

So while the Earth is about 4.543 billion modern years old, it may have revolved around the sun a significantly different number of times.

What is a reasonable estimate for how many revolutions - factoring in known geologic events - that the Earth has made around the Sun?

This question touches on the topic of orbital changes but never really answers what I'm asking here.
The second answer on this Quora question seems to answer my question but I don't know if that source is reputable, and the actual calculations and reasoning are not given
This reddit discussion touches on the subject but has differing / inconclusive answers


texts: Central temperature and pressure for constant density vs linear density model of stars

texts:
I just derived the pressure and temperature profile for a linear density model of a star. If I compare the profiles of pressure and temperature for a constant density model of stars, I see that the linear density model central pressure is higher, but the central temperature is lower.

What is the physical reason behind this?


texts: What visible differences do Geminids have to other meteors

texts: Unlike all other meteor showers, which originate from comets, Geminids originate from asteroid 3200 Phaethon. Seeing a large number of meteors last night, I noticed they seemed to be much more green than other meteors, but is there anything else I should expect to see different to other meteor showers? Brightness, size, length of trail etc?


texts: Could a rocky rogue planet get trapped in the orbit between Earth and Mars?

texts: I know it's extremely unlikely a rogue planet passing by there, and I know the size of rocky planets can vary a lot (IIRC there is a rocky planet 5 times the size of Earth) but in any hypothetical case, could a rogue planet be trapped in any part of the orbit between Earth and Mars? If so, which are the possible effects it could have over Earth and Mars? In which cases would they be expelled from the solar system?


texts: It may be surprising to know that all four giants in our solar system have rings orbiting around them.  Yet only Saturn has a system of rings visible to the naked eye.  Why is that?  What's so different about Saturn in comparison to Jupiter, Uranus and Neptune that makes it the only planet to have a visible ring system?


texts: I am a complete novice when it comes to astronomy, but someone asked me the above question casually. It seems as though planets are all roughly spherical, whereas other celestial bodies aren't necessarily. Is there are particular reason for this?


texts: Do heavier elements breakdown during supernova?

texts: Heavier elements like gold, uranium etc. are formed at the end of a star's life. As the star explodes into a supernova, it gives rise to nebula which is the birthplace of new stars. But as the star has already fused lighter elements into heavier elements, where does the new hydrogen required for the formation of new stars come from? Do heavier elements breakdown during supernova or is it some other process?


texts:
On the following page,

http://www.uni.edu/morgans/astro/course/Notes/section2/spectraltemps.html

It mentions Main, Giants and SuperGiants.

However for Dwarf Stars (e.g. D, Sd) , do I apply Main Sequence to the solar type?

For other types, IV, II, do I apply Main Sequence / Subgiant / Giant to the type?

If you look at the linked webpage, you'll see it mentions Types (V,III,I) but for instance where would Procyon (F5IV-V), Sargas (F1II) fit or should there be a different table for types IV, II?

Would groups (D, sd, IV,m II) have a different table?  Rigil Kentaurus (G2V) would clear fit into Main Sequence.


texts:
I am new here, and hope to state the question well.

In Islam, it's known that the Lunar Month starts if the Moon is sighted after the sunset of the 29th day of that month.

If someone claimed that he sighted the moon before the conjunction or if the moon sets before the sun, then this claim is certainly false.

My question is, what is the least conditions on the possible visibility of the moon?

There are many criteria that confirm the impossibility of sighting the Moon, but many people still claim the sighting. Which one is wrong?


texts: The field of astrobiology specifically discovering other planets that revolve around the sun-like star (also known as Exoplanets) has risen since 1990, but certain orbits of exoplanets are observed to have a much wider range in eccentricity than exhibited by the planets in our solar system. What's the reason behind this?


texts: Radio loud AGN restarting as Radio Quiet AGN?

texts:
Is it possible for a Radio-loud object (eg., an FRI galaxy) to evolve into a Radio-quiet (eg., a Seyfert) source?
Also, can this happen via AGN restart? That is, have there been instances where the active nuclei in a Radio-loud object switches off, and then restarts as a weaker Radio-quiet source?


texts:
I want to build a reflecting telescope in my home. I've attached a drawing of my plan that contains some explanations of what I understand so far, and highlights the parts of the design for which I have questions.

What type of mirror should i use, parabolic or spherical, and what are the factors considered when making that decision?

Does the glass used to make the mirror affect the incoming light rays? What about the secondary mirror in the middle of the tube?

Are there other things to consider that would help for higher magnification?

Some telescopes have a glass window at the front where light enters the tube, why is that? Would I need to add it here?


texts: Dynamical modelling of galaxies with counter-rotating components using the Schwarzschild method

texts:
I am currently trying to understand dynamical modelling using Schwarzschild's method. I have been doing some reading the past days, but I suspect that I am getting something really wrong. According to my current understanding, the Schwarzschild method for dynamical modelling using spatially-resolved kinematic data works like this:

Fit one or more 2D profiles (e.g., Gaussian) to the image or zeroth moment of the observation.
De-project the above fitted model to 3D space and create a 3D luminosity distribution.
Convert the 3D luminosity distribution to mass using a bunch of mass particles.
Create a series of possible orbits for the above mass particles and calculate the resulting velocity vectors.
From the above velocity vectors create velocity and velocity dispersion maps and calculate the chi-squared between them and the observed velocity and velocity dispersion maps.

The last step is what troubles me. To my understanding, the orbits of the particles in a Schwarzschild model can be counter-rotating. Right? In a galaxy observation, when we have two collisionless components (e.g., stellar components) that counter-rotate, it is possible that we will observe double-peaked spectral lines. Right? This information is impossible to be stored using a velocity and a velocity dispersion map, but it can be stored in a spectral cube. Yet, all papers on dynamical modelling using the Schwarzschild method fit models to velocity and velocity dispersion maps instead of a spectral cube.

So, from the above I have concluded that my understanding of the Schwarzschild method is not correct. I would really appreciate if someone could help me to understand what I am getting wrong.

Thank you in advance.


texts: More recent data and simulations of "Milkomeda", the collision of the Milky Way and Andromeda galaxies?

texts:
The Space.com headline Hubble Telescope Spots Two Galaxies in a Doomed (but Dazzling) Dance; The galaxies will ultimately crash into each other was probably overstated as seems to be policy in some popular press sites. The galaxies are not "doomed". However the paragraph below is interesting:

  Our Milky Way, for example, is on an inevitable collision course with the neighboring behemoth galaxy — Andromeda. Individual star systems like ours will likely be largely undisrupted, but distant observers will see the two galaxies gradually become one in some four billion years. ESA nicknames this new merged galaxy "Milkomeda."

Question: How much more is predicted now about the "upcoming" collision and possible merger of the Milky Way and Andromeda galaxies than has already been described in this answer's citation of a 2012 Astrobites review The Fate of the Milky Way? What measurements (if any) have contributed to this additional level of prediction?

  The current data could be improved by future additional HST observations. Also, soon it will be possible to compare them with independent water maser measurements for individual sources in M31 (see this Letter), which might allow measurement of other cool effects, such as the M31 proper motion rotation, and the increase in Andromeda’s apparent size due to its motion towards us.


texts: Can we identify planets, moons, and large asteroids in our solar system have a unique spectroscopy?

texts:
I'm looking to create a database of relatively consistent measurements for various cosmic bodies. Please inform if there's a way to gather reproducible signatures, with the same set of instruments to derive the same measurements within a given margin of error.
If also possible, please link to an academically-trusted data source.


texts: What changes are being made to VIRGO and LIGO (if any)?

texts:
Gravitational wave detectors VIRGO and LIGO are currently down for some updates, slated to be completed sometime early next year (they hope). What exactly are they doing? I hadn't heard it was down again after the last set of updates awhile ago. What are they updating now-- is that knowledge public domain?

Source: I went to an astronomy club meeting and it was stated in the presentation.


texts: Are there a lot of collisions between stars in the core of the galaxy?

texts: I'm reading on Wikipedia about Halo Stars that orbit the center of the galaxy at a high inclination away from the plane of the Milky Way.  It seems that at some point, these stars must dive back into the core of our galaxy at very high relative velocities.  This causes me to wonder...wouldn't this, combined with the greater density of stars in the core, cause a large number of stellar collisions in the galactic core?


texts: Are the distances between two celestial bodies the distance of their centers?

texts:
For example, the average Sun-Earth distance is 1 AU. Is this

the distance between the center of the Sun and the center of the Earth
the distance bewteen the surface of the Sun and the surface of the Earth,
or something else?


texts: I saw 3 consecutive object disappearing in the sky at same nearby location

texts: I was roaming on my terrace and I saw star-like moving object that gradually became small, red colour and disappear. Within a few minutes I saw another similar-looking  object a little distance away coming from opposite of first one and disappearing with red colour at nearly the same location. Within 5-6 minutes, I saw another similar object that soon disappeared. The object was moving from a lower altitude to a higher one. What was it?


texts: Stars give off light and are visible at nighttime but Planets do not give off light . So why are Planets visible at nighttime ?


texts: In what manner is the spectrum of a black body really a continuum?

texts:
Usually they say the spectrum of a black body is a continuum and emits radiation at every frequency. Is it really a continuum like a line or are there (small) intervals?

For example, can a body emit at 700nm and also at 400nm and everything in between, or at very small intervals like at 400.000001nm and 400.000002nm etc.? So is it really like a wave or line which implies a kind of infinity of wavelengths or is it more or less like discreet lengths although very close to each other? Or is it not really known because measuring is in a certain way always with discreet numbers (like 400.0001)?

As I understand it, it should always be at certain discreet numbers, firstly because the electrons from which the radiation comes only have a discreet values, and secondly because collisions between atoms/protons/electrons create energy at certain set wavelengths. But that is just my interpretation.

So what is the reality of black body radiation?


texts: Can Einstein-Rosen bridges - if they exist - link two points of which one lies outside of the observable universe of the other?

texts:
So there's stuff very far away that is, due to expansion, accelerating away faster than the speed of light, so fast that its light will never reach us even with infinite time - and we can't reach that point even if we travel at the speed of light for all eternity. The comoving distance of where the universe becomes fundamentally unexploreable is, afaik, some 46.5 billion light years or so.

Theoretical Einstein-Rosen bridges could connect any two points of space-time. What I wonder though is whether this could also apply to points that are farther than these 46.5 billion light years apart, or whether this is a theoretical maximum distance for wormholes as well?

Whether the answer is yes or no - an explanation would be great :)

Edit: maybe I'm mixing up observable universe and hubble volume here - I mean the one relevant to the question of course :)


texts: How space scientist keeps the track of the stars?

texts:
In billions of stars, how space scientist keeps the track of the stars ?

There is a star called KIC 8462852, I saw that picture, star is so small from the earth. It has higher chance to miss that star in the universe.


texts: What is the spectral energy distribution (SED)?

texts:
I see the SED being referred to as several different things and now I am confused about what it actually is and what are its units. In particular, I find the SED Wikipedia page not understandable.

The Flux $F$ of a star/galaxy is related to its luminosity $L$ by
$$F=\dfrac{L}{4\pi d_L^2}\,,$$ where $d_L$ is the luminosity distance.
If we differentiate the quantities and remembering that the emitted wavelength $\lambda_{em}$ is related to the observed one by $\lambda_{obs}=(1+z)\lambda_{em}$, where $z$ is the redshift, we can have two quantities:

$\dfrac{dF}{d\lambda_{obs}}\equiv f_{\lambda}$
$\dfrac{dL}{d\lambda_{em}}\equiv l_{\lambda}$

I think $f_{\lambda}$ is the specta (units of [Energy][Time]$^{-1}$[Lenght]$^{-3}$) and $l_{\lambda}$ is the SED (and therefore has units of [Energy][Time]$^{-1}$[Lenght]$^{-1}$). Is this correct? Can you give me some resources (eg. papers or books) where this is written down? Thank you.


texts:
I am pretty new to astronomy and the project I am currently working on requires some knowledge of equatorial coordinate system.
As long as I have been researching this question, I understood that vernal equinox is the origin of this system. At this moment I am stuck with task of finding distance on celestial sphere between west(on horizon) and vernal equinox.
So, how do you count this distance?


texts: Where can I find thousands of actual images of stars in the galaxy?

texts:
I'm trying to write a program to differentiate between images of stars and nebulae. However, I'm not able to find a large enough dataset of actual images of stars that I can use to train my deep learning algorithm. Is there any database that has thousands of actual images of stars that I can use to train my deep learning algorithm? Thanks.
EDIT: I need individual images of stars so that my program can learn the identifying features of a star and be able to differentiate a star from another celestial object.


texts: How would tidal effects behave in this setup: An icy moon orbiting a gas giant, as the gas giant orbits a red dwarf?

texts:
Let me know if this is more appropriate for worldbuilding.

Essentially, I'd like to know how tidal effects would behave in these circumstances (if it's even stable):

An icy moon orbiting a gas giant, with the gas giant orbiting a red dwarf.

Here is a detail that may manipulate the answer:

I want the moon (if possible) to live in the red dwarf's habitable zone. It's okay if it periodically leaves the habitable zone, so long as it returns.

I just need to know where tidal locking occurs (if at all), and how the moon receives most of it's heat (through internal heating like tidal forces or though external heating via the red dwarf).


texts:
Comets are commonly called icy dust balls or dirty snowballs and as such rather light:

Known comets have been estimated to have an average density of $0.6 {\rm g}/{\rm cm}^3$. Because of their low mass, comet nuclei do not become spherical under their own gravity and therefore have irregular shapes.

I read about their live times, I learned that they can rotate, how they can be classified by their type. NASA summarizes the key facts as follows

Comets are frozen leftovers from the formation of the solar system composed of dust, rock and ices. They range from a few miles to tens of miles wide, but as they orbit closer to the sun, they heat up and spew gases and dust into a glowing head that can be larger than a planet. This material forms a tail that stretches millions of miles.

What interests me has to do with their formation. I know that comets are not spherical and rather small in size. I am now wondering how comets' nuclei stick together, more specifically if there is some empiral knowledge or even some theory I should know about. Obviously, gravitation is not strong enough, so it must be merely the structural stability of the material, but how can that be estimated?
References

Press Release of the Max Planck Society: Are comets more like "Icy Dust Balls" or "Dirty Snowballs"? (2005)
The creation of comets
Can two comets travel together as one?
How big do comets get?
Why did the Comet Shoemaker-Levy-9 fragments cause such large explosions on Jupiter?
The article from the Scientific American If comets melt, why do they seem to last for long periods of time?


texts: Generating random galaxy catalogs for correlation functions

texts:
The galaxy correlation function, when computed directly from a galaxy catalog, relies on computing a randomly generated counterpart catalog.

When dealing with a simulated galaxy mock-catalog, where the sample of galaxies is roughly uniform over a large box (e.g. the galaxy mocks created from Millennium/Millennium II), the random catalog can be just be a uniform distribution of points in the same volume as the real data.

However, real-world galaxy catalogs are not homogenous boxes, and have very irregular shapes and observationally induced redshift and angular distributions. Even some mock-catalogs are endowed with these properties to better represent real data. In these cases, how is a random catalog best produced? With some sort of probability distribution in coordinates which attempts to mimic the "non-physical" (i.e. not due to observational constraints) part of the distribution? Or a simple binary mask which filters out empty regions, but otherwise leaves the random catalog uniform.

If the answer is that some nonuniform distribution should be used, is there a usual method for doing so? The literature I have found (e.g. for the SDSS published data, and for galaxy mocks mimicking SDSS's constraints) does not discuss this in any way. Note, if this is a highly involved process beyond a brief summary and a source or two, I do not expect a full answer here. Rather, I am trying to determine if there is an existing set of standard methods which are documented but have eluded me thus far.


texts: Why aren't corrector plates aligned with the center of curvature in an SCT?

texts: According to wikipedia, Schmidt corrector plates must be aligned with the center of curvature to eliminate the spherical aberration. However, in compact SCT designs by Celestron and Meade, that is clearly not the case since the optical tube is usually shorter than the radius of curvature of the primary mirror. My question here is WHY?


texts:
Recently I've found that some post-AGB objects are spectrally classified as hot luminous stars. For example, in the Toruń catalog of post-AGB objects, the star LSE 63 is listed as both a post-AGB and a B1Iabe.
I thought that post-AGB objects were the result of the evolution of low- and intermediate-mass stars. On the other hand I also thought that a B supergiant could only be an evolved stage of a massive luminous star. How can both be true at the same time?


texts: Do we see stars from other galaxies (not Milky way) in the night sky with the naked eye?

texts:
I saw reports that only Andromeda Galaxy and Big/Small Magellanic Cloud galaxy stars could be visible with the naked eye (how many stars would be from them out of a few thousand visible?)

This question appeared because there are some very "sparse" galaxies (very few stars in them) and scientists say night sky in them is practically all black (starless)...

So is it true that 99,9% visible stars in the night sky (naked eye) are from the Milky Way only?


texts: can we use connect a long pipe with space station and use vacuum for fuel transfer?

texts: We all know that we need a lot of fuel to escape from earth. Even 90% fuel of an spaceship is wasted in escaping the earth which definitely affect our power to explore the universe. we have to do a lot of calculations and even a small failure can waste a lot of money. for ex- the Manglayan Indian mission to Mars due to under performance of the engine was almost lost. As it a cheapest mission to Mars. They have a very limited fuel. So why can't we connect our space station with a long pipe and Make our space ship refuel at that point. I know a lot of energy will be required to pump the fuel up. But I was thinking about a better option. why can't we use vacuum to transfer liquid. Like if we have a pipe and we suck one end and the water automatically travels. Is it possible or what are the technical difficulty here.


texts: How can I get/generate/extract PSF image from galaxy .fits image?

texts:
I want to model an image of a galaxy from Hubble.
For this, I need the PSF image as well.
I already tried to use TinyTim, but I don't have half of the parameters and cant be sure about the quality of output.
Is there any way for me to get it from the .fits image of a galaxy?


texts: To what extent do the spin of smaller celestial bodies reflect the spin of the larger system’s of which they are a part?

texts:
One can ask whether two objects are spinning in the same direction or not. For example, the Sun, Earth, Luna, most of our solar planets (except Venus and Uranus), and the planets’ satellites all spin in approximately the same direction. Likewise, the orbits of these bodies are in the same direction.

I understand that the rotational plane of our solar system is tilted about 60 degrees relative to our galaxy’s. If you project one rotation onto the plane of the other, I have the impression from maps that they may have opposite orientations — i.e. if we face north to south, our solar system’s rotation is counterclockwise, and our galaxy’s rotation is clockwise. Correct? What about the rotations at other scales of the larger systems we are in, such as our local star cluster, our local galactic cluster, and so forth? Thank you.


texts:
I guess we will need to take our lunch to Mars for some time before we are able to produce food there! But do we need to take a saltshaker too?
Can we extract editable salt from the crust of Mars, Moon, Titan or Europa?


texts: This article says the moon may start moving closer to the Earth in the distant future; could this be true?

texts:
Bruce Dorminey wrote an article for Forbes with the title of "Earth And Moon May Be On Long-Term Collision Course". The article notes:

"For now, our anomalously large Moon is spinning away from us at a
variable rate of 3.8 centimeters per year. But, in fact, the Earth and
Moon may be on a very long-term collision course --- one that
incredibly some 65 billion years from now, could result in a
catastrophic lunar inspiral."

It seems a little illogical that the Moon would suddenly start running toward earth at a far distance. Multiply 3.8 by 65 billion you get 2,470,000,000(May be innacurate). The article also notes this:

"As a result, the timing of the Moon’s ongoing recession is hard to
precisely predict. That’s because, as Barnes1 points out, the Earth
goes through glacial and interglacial cycles, causing the area of
shallow seas to change as sea level rises and falls."

Is it possible to understand how/why the author believes that the Moon could fall into a lunar inspiral? Please cite sources, thanks!

1Jason Barnes, a planetary scientist at the University of Idaho


texts: How to align equatorial mount in the Southern Hemisphere?

texts:
I'm new to astronomy and recently got myself a telescope with an equatorial mount. I've found lots of resources online showing how to align the telescope but they all operate on the assumption that you live in the Northern Hemisphere and align to True North or Polaris.

What is the procedure for those of us who live on the other half of Earth? Pointing my telescope north, I still suffer problems finding and tracking objects in the sky.


texts: How does water exist within the frost line of a star?

texts:
My supposition is that within the distance of the so called frost line around a star, water in empty space sublimates, evaporates. I further suppose that this means that vaporized water is pushed to outside the frost line by solar wind or some other mechanism. (Please correct me if this is wrong)

But there are some ways for water (not necessarily liquid) to exist within the frost line. I wonder under what conditions that is possible. What the origin or history such water can have. And how common or likely it is.

I suggest some possibilities to be extended, elaborated or refuted:

Water under enough atmospheric pressure to keep it from escaping into space.
Water in cold shadow, as in some craters on the lunar poles.
Water inside rock, as in the mantle of the Earth (and other planets?)
Water ice transported by comets across the frost line.
Water vapor hanging around in empty inner inter-planetary space, for example after a planetary collision which melts most matter into a cloud. Or maybe permanently.


texts:
Is there any way to calculate declination of Moon for any day?I'll subtract inclination of Earth on the ecliptic from the result. I'll get Moon's the shortest angular distance from Sun.
Thanks for all answers!


texts: For chemical reactions occurring in the interstellar medium, which involve metal-ions, will the metal ions be solvated or not?

texts: Usually, metal-ions in terrestrial chemistry will be solvated - either by gas-phase solvent molecules or by liquid-phase solvent molecules. But the interstellar medium (ISM) is never in local thermodynamic equilibrium. Moreover, the solvation of any system is driven by the system's proclivity to attain thermodynamic stability. But given the lack of local thermodynamic equilibrium in the ISM, solvation should not at all be an important factor in the ISM. Is it right or wrong? Any reference from the Astrochemistry/Astrophysics community will also be highly appreciated.


texts: Does one need to take into account finite gravity speed in N-body simulations?

texts:
Most small-scale N-body simulations (e.g., planetary systems, solar system, stellar clusters, ...) use  classical Newtonian gravity.

Most large-scale N-body simulations (e.g., galaxy clusters, ...) use general relativity.

My question: if I were to make a large-scale N-body simulation using Newtonian gravity, would it be enough to "correct" that to first-order by modifying the equations of motion to take into account the fact that gravitational fields propagate at the speed of light?


texts: Since when do astronomers have the notion that space is void?

texts:
Since when do astronomers have conjectured that space is void, and not full of air like our immediate environment?
I am more interested about how long the notion has been around and how influential rather than when and how it has been scientifically demonstrated.
Background for the question: I heard a conference about philosophy of science explaining how Galileo revolutionized physics by postulating principles that where true, but defying immediate observation, like "all objects fall with the same acceleration" when in fact heavier ones tend to fall faster due to air resistance, or "undisturbed objects move in a straight line at constant speed" when such a trajectory can't be observed on Earth because of gravity and frictions.
I was wondering how he came to have these notions, then thought he might have been inspired by the motion of planets because he knew them very well and they move in a void so their movement is, as far as a XVI century astronomer is concerned, undisturbed.
But that would imply he knew space is actually void of air, which is not intuitive and requires observation technology he did not have access to (planes, weather balloon, sounding rockets...). So i was wondering since when this fact have been established or at least conjectured.


texts: How do I adjust the sunrise equation to account for elevation?

texts:
I have been working with the sunrise and sunset formula, using the equations from Wikipedia. The problem is that, in my usage thereof, it seems that it only works for sea level; if I start with coordinates that correspond to any point above sea level (or below, for that matter), it will still output the sunrise and sunset for my coordinates at sea level.

For example, today (21/01/2018), in Denver, CO (~1mi above sea level), sunrise was at 07:15:28. Yet my equations keep yielding 07:15:41, which is exactly on-target, were Denver at sea level. How do I account for the fact that higher altitudes experience sunrise earlier than lower altitudes of the same coordinates?


texts: Suggestions for a beginner-friendly telescope

texts:
I'm hoping someone can point me in the right direction for a beginner-friendly telescope for my family.

My husband has mentioned wanting a telescope off and on for a few years, but he's never delved into the idea enough to give specifics. We have an autistic 7-year-old who has developed a Special Interest in astronomy, and since it's our practice to delve into his SI's with him, it seems like a good time to take the plunge.

Pertinent information...

We live in a major metropolitan area -- in the suburbs about 30-45 minutes from downtown Chicago. We will be able to drive to a less light-polluted area from time to time, but realistically, we'll be seeing what we can see from the yard or second-story balcony most of the time.
7yo will likely be most interested in objects seen with some degree of detail -- planets, stars, comets, our moon, other brighter objects. We adults would like to glimpse some of the dimmer objects as well, though we know they'll be faint. 7yo will likely be impressed by glimpsing those objects, as well, since he's a bit obsessed with the vastness of the universe at the moment.
We are true beginners. Think of people who have never touched a scope. But we're patient and smart, so we can learn. Which is kind of the point, I suppose.
7yo is not always patient, so an easy, quick set-up would be desirable.
No children will be using the scope unsupervised, but we will be teaching 7yo how to use it while closely supervised.
If giving specific recommendations, we'd like to keep the cost under $500US.


texts: Why does this graph for sunlight intensity on land has a steeper slope during sunrise as compared to sunset?

texts:
I got this image while checking weather data for a city in North India using  Mathematica's Wolfram Alpha query

I noticed one feature in the graph which i could not explain .
Why does the encircled part 'A' which denotes  sunrise has slightly higher slope as compared to encircled part 'B' which denotes sunset !

I also checked the graph for summer month and the pattern was exactly opposite

Summer Month

Am i interpreting the data wrong or is it so that sun achieves its highest intensity during the day faster in winter months than in summers ? What could be the reason behind this ?


texts:
When checking the collimation of a Celestron 14" SCT I took this image:

My question is: how much will the particles causing the local aberrations affect the image quality? (i.e. do I need to clean the optics?).


texts: Am I using my Celestron 8 Schmidt-Cassegrain telescope correctly?

texts:
I became interested in astronomy a few years ago and started with a Celestron AstroMaster 70AZ refractor telescope. That seemed nice, and I wanted to upgrade to a go-to telescope that was also more much more powerful, so I bought the 8 inch Celestron Schmidt-Cassegrain.

It's great, but honestly I'm a bit disappointed because the magnification doesn't seem all that much stronger than my 70AZ. I haven't done a side by side comparison. But for example when looking at Saturn, I was expecting to see more than just a white ball with a ring around it - I was able to see that with my 70AZ. I thought I'd see colors, and maybe be able to differentiate between some of the bigger ring bands.

I haven't tried any deep sky objects. I'm using various lenses starting from 30mm down to 6mm.

Am I doing something wrong?


texts: I'm on the most northern part of Germany (Schleswig-Holstein) it is 11.20pm right now and the moon is here as bright as I never saw it before I was just outside and it is as bright as if it was dim daylight. When the clouds moved away from the moon and I looked into the moon for a little moment it was so bright, that it actually glared me for a little moment. Is there anything specific going on that is just favored this event? Or is it something that simply happens sometimes and I just never noticed it before?


texts: In what ways are neural net classifiers "better" than search algorithms for eclipsing star system searches? (1D time series, not images of cats)

texts:
Neural net classifiers are both "hot" and useful.
TIC 168789840: A Sextuply-Eclipsing Sextuple Star System is quite an interesting read, and describes the use of one trained on a supercomputer to look at historical TESS data and build a catalog.
Discussion of the model can be found in Section 2.
The mechanics and optics behind mutually eclipsing star systems is well understood and in my naive thinking could be described algorithmically.
The limits of a resulting catalog from such an algorithmically-designed search could be understood statistically; one knows the constraints in terms of brightness ratios, periods, inclination deviations etc. so one should have an idea of which systems should pass and which should fail.
A neural net classifier is pretty much a black box. It can be tested on an artificially designed dataset to check its behavior, but that may turn out to be fairly lumpy; in a group of similar cases some may pass and some may fail and the reasons may not be clear, you can't query a large super-computer class neural net and ask "Why didn't you like this one?" in an easy and transparent way.
Question: For 1D time series data of predictable orbital mechanics and optics, (as opposed to sets of images that may or may not contain cats) in what ways (if any) are neural net classifiers "better" than search algorithms for eclipsing star system searches? Are there any advantages, or is this simply an alternative technique worthy of investigation?


texts:
Suppose I want to build or buy a telescope for the following uses:

Astrophotography (mainly galaxies and nebulae).
Transits of exoplanets and binary systems like Cygnus X-1.
To search for BH+star systems.
To measure the rotation curve of some spiral galaxies

Is that ALL feasible and/or cheap at amateur/semi-amateur level?


texts:
It is often said that the Sun is a medium size, or even dim star. Is this true?

According to this list of stars within 21 light years, there are, out of the closest 121 stars, only six brighter than the Sun. This means that the Sun is in the top 6%. If you also count brown dwarfs, the Sun ranks even higher.

Doesn't this indicate that the Sun is actually a relatively large star?


texts:
August 21 is going to see a total eclipse across most of the US, and I'm planning a trip to what I hope is an ideal viewing location.

What are good ways to safely view the eclipse?

I don't want to make a big trip out of it, only to be looking into a poor quality pin-hole shoebox, or $2 mirrored cardboard glasses.  How can get I get a good, detailed clear view of it while staying safe?  What about ways to photograph it effectively?


texts: How do a planet's moons and a planet's rings interact?

texts:
I am making a video game which features a planet and its moon. And I thought I would add rings too.

But that got me wondering... how do a planet's moon and a planet's ring influence each other?

Does a moon clear out all the debris in its orbit? In other words: does it make a gap in the ring? If so, how large is the gap in relation to the moon's radius?

If not, does the moon travel along as all the other matter in the ring? Would it not make the debris fall to the moon, thereby growing the moon?

Lastly, are both the rings and moons typically in the same plane?


texts: Computing the over-density of Lyman-alpha emitters

texts:
Let's assume that I have observations of $N$ galaxies in a projected area $A$, within a redshift range $\Delta z = z_{max} - z_{min}$. What is the correct way of computing their number volume density? I guess the volume has to be derived multiplying $A$ by the differential Luminosity Distance $D_{L}$ computed at $z_{max}$ and $z_{min}$, i.e., $D_{L}(z_{max}) - D_{L}(z_{min})$, but I am not sure.
Also, what is the more appropriate way of evaluating the "significance" of any over-density.
For instance, assuming that the observed galaxies are Lyman-$\alpha$ emitters, does it exist any computation of the "standard" number density of Lyman-$\alpha$ emitters, to compare with?


texts: And why is it moving? Doesn't make very much sense to me, a moving antenna. Or is it kind of radar that is checking  for dangerous objects? These are screen shots from this YouTube video.


texts: When examining an exoplanet's atmosphere is the star's emission spectra or planet's light used?

texts:
My understanding of the main method we use to figure out an exoplanet atmosphere composition is that when a exoplanet transits their sun, visible light passes through the planet's atmosphere, and absorbed by the elements in the atmosphere. We then observe these absorption lines to figure out the chemical composition right? Or am I getting some details wrong here?
My main question is, does the light that passes through the planet's atmosphere is the sun's light or the sun's emission spectra?
Also will different stars starlight cause different absorption lines? As in say some planet X orbiting a M class star as opposed to the same planet X orbiting a G class star. Considering both the stars are different but the planet are same, would the absorption bands of the planet be different in each case?
References

ESA: Starlight yields clues to exoplanets’ atmospheres
Lecture by  Michael Richmond: Spectroscopy of exoplanets/spectra/spectra.html


texts: If you looked at Earth while travelling at relativistic speeds, will you see sped-up activities?

texts:
Suppose you traveled off Earth and back at relativistic speeds, so that when you come back much longer time elapsed on Earth than you experienced. Suppose you had an excellent telescope through which you could observe the details of the surface of the Earth down to human scale, all the time.

What will you see?  Will you see people moving incredibly fast? Will you see people progressing from birth to old age in a matter of seconds?


texts: What is the orbit of Earth around the Sun?

texts:
According to wikipedia and other sources, a planet and a star always move in a circular orbit around the common center of mass of the both bodies, in case  of Earth and sun, this center of mass lies inside the sun. Therefore, Earth should orbit the sun in a circular orbit. So, my question is, why does the Earth orbits the sun in an Elliptical orbit?

And, if it does, and one focus is the sun, then what is the other focus?